This invention relates to a method for producing a high surface area washcoat are suitable for use as supports for catalysts. The washcoats are made essentially of AO-Al.sub.2 O.sub.3 wherein A is Ba and/or Sr. The high surface area is achieved by a method which involves forming the AO-Al.sub.2 O.sub.3 by contacting element A in the ionic form with an aluminum oxide yielding species followed by firing to result in the A being homogeneously distributed throughout the Al.sub.2 O.sub.3. The high surface area is maintained over long periods of time under conditions of high temperature which are encountered in applications. The washcoated substrates provide supports for a wide variety of catalysts. The washcoat can be impregnated with a catalyst metal precursor which is fired to form a highly dispersed catalyst. The high surface area afforded by the washcoated substrates preserves the active sites for the catalyst, especially the catalyst metals, thus prolonging the life of the catalyst.
Catalysts for the oxidation of carbon monoxide and hydrocarbons, and for the reduction of nitrogen oxides of automobile exhaust emissions, are dispersed on washcoated metal or ceramic monoliths as automotive catalytic converters. Cerium oxide and/or cerium nitrate is usually mixed with gamma alumina to help improve catalytic performance, by providing oxygen under rich fuel conditions and is used also in a washcoat to increase dispersion of the metal catalysts, enhancing apparent catalytic activity The surface area of gamma alumina decreases significantly during the aformentioned catalytic reactions at temperatures above about 600.degree. C. as the system ages. The result of this "washcoat sintering" is the loss of alumina surface area (and therefore adsorption sites for the metal catalyst). This results in a decrease of metal dispersion with a resultant lowering of catalytic activity.
It would be advantageous therefore, to have a high surface area washcoated substrate which can function as a catalyst support at high temperatures without any significant loss of surface area and activity.